The invention concerns a hypodermic needleless injection system for injecting a liquid medication.
International Patent Application with publication No. WO-A-98/31409 describes a hypodermic needleless injection system for injecting a liquid medication comprising a disposable medication cartridge and a reusable application device. The reusable application device includes a locking pressure chamber that contains and supports the cartridge, and other necessary subsystems including electric ignition and safety interlocks. The disposable cartridge contains a prefilled sterile single dose medication container and a small pyrotechnic gas generator that produces 200 to 300 bar pressure exerted on the medication container for carrying out the injection. The single dose medication container comprises a first region delimited by a thin walled, flexible plastic medication container and a second region having a jet nozzle. The gas pressure provided by the gas generator is applied on the thin walled container which collapses under that pressure and this causes ejection of the liquid through the jet nozzle.
In the known system disclosed by WO-A-98/31409 the thin wall of the medication chamber forms a barrier between the liquid medication and the high pressure gas. The latter thin wall is largely under hydrostatic pressure and carries only modest tensile and shear stresses. However in order to reduce the probability of gas contact with the liquid medication in the event of a single point failure of the thin flexible wall of the medication chamber, it is advisable to use a second wall, e.g. a rubber wall, which shields the thin wall of the medication chamber.
A disadvantage of the structure of the known system disclosed by WO-A-98/31409 is that it does not allow the use of low cost energy sources, e.g. mechanical devices or low pressure gas sources, for generating the necessary pressure on the deformable wall of the medication container.
This disadvantage thus raises the problem of how to modify the structure of the injection system in order that the modified structure allows the use of that low cost energy sources and allows thereby a reduction of the manufacture cost of the whole system.
The aim of the invention is therefore to provide a hypodermic needleless injection system for injecting a liquid medication which is adapted to make use of low cost energy sources and which thereby makes possible to reduce the manufacture cost of the injection system.
According to the invention this aim is attained with a hypodermic needleless injection system comprising:
(a) a medication unit configured and dimensioned to store a volume of liquid to be injected, said medication unit having a first region and a second region that are in liquid communication with each other, said first region being deformable and said second region having at least one orifice,
(b) a hydrostatic chamber containing a hydrostatic pressure transfer medium, said hydrostatic chamber being so configured and dimensioned that the medication unit is located at least partially within the hydrostatic chamber and so that a pressure exerted on said transfer medium would cause said first region of said medication unit to deform so as to reduce the volume available for said liquid medication within said medication unit, and
(c) a first piston having a first end and a second end opposite to said first end, said first end having a surface which is adapted for applying a pressure on said transfer medium contained in said hydrostatic chamber.
A preferred embodiment of a hypodermic needleless injection system according to the invention further comprises
(d) an activatable force generator able to generate a force and to apply said force on said second end of said first piston in order to cause that said surface of said first end of piston applies a corresponding pressure on said transfer medium, and
(e) and activation means for activating said force generator.
The main advantage of an injection system according to the invention is that it makes possible to attain the above mentioned aim. An additional advantage of a preferred embodiment of such a system is that it is apt to be manufactured entirely as a disposable injection system which can be provided to the user ready for use in a package which ensures sterility. In the context of the invention ready for use means prefilled with a predetermined amount of medication and without requiring any assembling step to be performed by the user before use.